ASVAB Mechanical Comprehension Practice Test 786247 Results

Your Results Global Average
Questions 5 5
Correct 0 2.70
Score 0% 54%

Review

1

Assuming force applied remains constant, which of the following will result in more work being done?

53% Answer Correctly

moving the object with more speed

moving the object with more acceleration

increasing the coefficient of friction

moving the object farther
Solution

Work is accomplished when force is applied to an object: W = Fd where F is force in newtons (N) and d is distance in meters (m). Thus, the more force that must be applied to move an object, the more work is done and the farther an object is moved by exerting force, the more work is done.

2 If the green box weighs 10 lbs. and is 4 ft. from the fulcrum, how much force would need to be applied at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 6 ft.?
62% Answer Correctly
26.67 lbs.
0 lbs.
6.67 lbs.
1 lbs.
Solution

To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

Rada = Rbdb

where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

Solving for Rb, our missing value, and plugging in our variables yields:

Rb = \( \frac{R_ad_a}{d_b} \) = \( \frac{10 lbs. \times 4 ft.}{6 ft.} \) = \( \frac{40 ft⋅lb}{6 ft.} \) = 6.67 lbs.

3 If the force applied at the blue arrow over 9 ft. moves the green box 3.0 ft., what is the mechanical advantage of this lever?
56% Answer Correctly
2.7
3
-2
4.5
Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where Ed is the effort distance and Rd is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{9 ft.}{3.0 ft.} \) = 3

You might be wondering how having an effort distance of 3 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 3 times the resistance distance, the effort force must be \( \frac{1}{3} \) the resistance force. You're trading moving 3 times the distance for only having to use \( \frac{1}{3} \) the force.

4 If the radius of the axle is 3 and the radius of the wheel is 6, what is the mechanical advantage of this wheel and axle configuration?
36% Answer Correctly
6
1
0
-3
Solution

The mechanical advantage of a wheel and axle lies in the difference in radius between the inner (axle) wheel and the outer wheel. But, this mechanical advantage is only realized when the input effort and load are applied to different wheels. Applying both input effort and load to the same wheel results in a mechanical advantage of 1.

5 If the green box weighs 55 lbs. and is 9 ft. from the fulcrum, how much weight would need to be placed at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 4 ft.?
63% Answer Correctly
123.75 lbs.
495 lbs.
0 lbs.
30.94 lbs.
Solution

To balance this lever the torques on each side of the fulcrum must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

Rada = Rbdb

where a represents the left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

Solving for Rb, our missing value, and plugging in our variables yields:

Rb = \( \frac{R_ad_a}{d_b} \) = \( \frac{55 lbs. \times 9 ft.}{4 ft.} \) = \( \frac{495 ft⋅lb}{4 ft.} \) = 123.75 lbs.